| About this Abstract |
| Meeting |
10th International Symposium on Superalloy 718 and Derivatives (2023)
|
| Symposium
|
Superalloy 718 and Derivatives
|
| Presentation Title |
Segregation and Freckles in Alloy 718 and Related Alloys |
| Author(s) |
Alec Mitchell, Stephane Hans |
| On-Site Speaker (Planned) |
Alec Mitchell |
| Abstract Scope |
The defect known as “freckle”, normally identified on billet sections, has been extensively studied by modeling and experimentation. It appears to form as an upward-flowing channel due to gravitational forces acting on the segregated liquid between the growing dendrites. This liquid is less dense than the bulk liquid in many superalloys. The Nb-containing superalloys (and several other complex alloys) also form freckles, but examination shows that they are channels of liquid which has flowed in a downward direction as the segregated liquid becomes more dense than the bulk. The mechanism proposed for the “upward” freckles does not fully explain the phenomenology of the “downward” freckles in several key aspects. In this work we propose that a different series of events leads to the “downward” freckle formation; a mechanism which more fully explains the observed facts. The conclusion is that the present direction of alloy development, that of composition manipulation to reduce the segregation density changes, is likely to be only partially successful and that changes in other process parameters will also be required. |
| Proceedings Inclusion? |
Definite: At-meeting proceedings |